Ceramic materials in monolithic honeycomb form offer the advantage of low pressure drop for automotive & stationary emissions control reactors, catalytic oxidation, adsorption, separation, and other applications. The ceramic materials can be extruded into cellular monoliths or coated onto a cellular ceramic substrate using conventional “washcoat” processes. Both extruded and coated ceramic substrates are prepared with a binder to promote interparticle adhesion and strength. For many applications it is advantageous to control pore structure, density, strength and surface area.

In this paper composition, fabrication and physical properties of cellular monolithic substrates will be reviewed. Emphasis will be on extruded materials used as catalytic supports for automotive, DeNOx and oxidation reactions.

Monolith perovskite catalysts of honeycomb structure for high-temperature applications are elaborated. Problems of powdered perovskites synthesis by efficient plasmochemical and mechanochemical methods as related to real structure and reactivity of these compounds are discussed. Pilot testing in reactions of fuels combustion, ammonia oxidation, methane conversion and sulphur dioxide reduction proved high activity and stability of these catalysts.

Monolith catalysts are effective for partial oxidation reactions at high temperatures at contact times between 10−4 and 10−2 sec. We summarize results for three reactions: (1) syngas by direct oxidation of CH4, (2) olefins by oxidative dehydrogenation of alkanes, and (3) HCN by ammoxidation of CH4, and we consider what features of monoliths create optimal selectivity with high conversions. Monoliths used are noble metal films coated on ceramic foams, extruded ceramics, ceramic fibers, and woven Pt-10%Rh gauze catalysts. Effects of metals and geometries of the ceramics are ceramics are compared to show how these factors influence activity and selectivity.

The primary use of reticulated ceramics is in molten metal filtration. However, other applications have emerged which utilize the porous nature of these materials, including low mass kiln furniture, low NOx. infrared burners, gas diffusers, hot gas filters, sensors and catalyst supports. In this paper, the use of reticulated ceramics as catalyst supports will be reviewed with emphasis on the manufacture, structure and properties.

Successful catalyst supports must fulfill different requirements simultaneously [1]. By serving as a base for catalytic components, they provide good activity and selectivity, but certain physical properties are equally important. For example, small catalyst particles are desirable in order to avoid external heat and mass transfer limitations and to provide high effectiveness for the active component dispersed throughout the particle. However, small particles pack with low bed porosities and unacceptable pressure drop results. Open-pore ceramic foams show promising properties that could overcome these difficulties. They have good high temperature resistance, low bulk density and tortuous flow patterns, together with open porosity as high as 85% formed from megapores 0.04 to 1.5 mm in diameter [2]. Characteristic parameters include cell size, window size and surface area, all correlated with the number of pores per inch [PPI]. Ceramic foams were first used as molten metal filters [3,4] and catalytic combustion devices [5–7]. Catalytic applications are beginning to appear and these have been reviewed by Twigg and Richardson [8].

The new method of preparation of La1−xSrxMnO3 catalysts supported on ceramic foam materials was developed. The synthesized supported perovskite catalysts were examined by X-ray diffraction analysis and BET methods. It was shown that in coated samples there is a pure perovskite phase on the support surface up to temperatures of 1000°C.

Unsupported La1−xSrxMnO3 catalysts were synthesized applying co-precipitation technique using La, Sr and Mn acetylacetonates and were studied by X-ray diffraction analysis. Temperature programmed reduction method revealed that catalysts contain 2 types of active centers: low temperature (α) and high temperature (β), the quantity of these centers and correlation between them depend on the value of x. It was shown that supported perovskite catalysts, similarly to the massive ones, maintain two types of active centers (α and β).

The activity of La1−xSrxMnO3 on mullite foam was characterized in the methane oxidation reaction.

Using sol-gel processing techniques it is possible to vary the condensation pathway over wide ranges to form primary species ranging in structure from oligomers to polymers to particles. The porosity of the corresponding dry gels depends on the size and structure of the primary species, the organization of these structures, often by aggregation, to form a gel, and the collapse of the gel by drying. This paper reviews these ideas in the context of forming thin film or bulk specimens. Several strategies are introduced to control porosity on length scales of interest for catalysis and catalytic membrane reactors: 1) aggregation of fractals; 2) management of capillary pressure; 3) surface derivatization; 4) relative rates of condensation and evaporation; 5) the use of organic templates and 6) sintering. These strategies are contrasted with the more traditional particle packing approach to preparing controlled porosity materials.

A sol-gel based preparation of a mixed oxide allows considerable control over the extent of component mixing. When the reactivities of the alkoxide precursors are evenly matched, a homogeneously mixed sample can be produced; a large reactivity difference results in a segregated mixed oxide product. We have prepared and characterized two sets of mixed titania-silica aerogels, each covering the entire composition range. One set was made using silicon precursor prehydrolysis to minimize the reactivity difference and promote homogeneous component mixing; the second set was made without prehydrolysis.

The catalytic properties of pillared clays for organic chemical conversions, especially those occurring in liquid media, can be substantially improved by surfactant modification of the pore structure during the pillaring reaction. For instance, the incorporation of a non-ionic surfactant, such as the alkylated polyethylene oxide C12–14H25–29O(CH2CH2O)5H, in the synthesis of alumina pillared montmorillonite results in a dramatic increase in the interparticle (textural) mesoporosity of the final calcined products. These surfactant-modified mesoporous pillared clays are exceptionally active as catalysts for the diffusion controlled liquid phase alkylation of biphenyl. The enhanced mesoporosity facilitates access of the reactants to the active acid sites in the interlayer nanopores of the pillared clay tactoids. Organic polymeric molecules also can be used to mediate the pore structure of pillared clay materials. The reaction of aluminum chlorohydrate oligomers with Na+ rectorite in the presence of polyvinyl alcohol as a pillaring precursor affords a supergallery alumina pillared rectorite with a basal spacings of 52 Å and a corresponding gallery height of 33 Å under air- dried conditions. A stable gallery height of 23 Å is observed even after treatment with 100% steam at 800°C for 17 hour. The new supergallery intercalate is characterized by a surface area, pore volume, and catalytic cracking activity superior to conventional alumina pillared rectorite and related smectites with 9 Å gallery heights.

We developed a model to describe the morphology and energetics of pillared clays. Grand- Canonical Ensemble Monte Carlo and Molecular Dynamics simulations are used to study diffusion and adsorption of finite-size molecules in such systems, and the effect of various factors on these processes is investigated.

Two types of synthetic hydrotalcite-like [Mg6Al2(OH)16 ][An−%D;2/n (HT) were prepared where A = Cl− anions (Cl-HT), and NiC42− complex anions (NiCl-HT), in order to examine: (1) the reactivity of Cl− anion (or ligand) towards alkyl halides and (2) their catalytic behavior in the Finkelstein reaction. For instance, 0.4 g of NiCl-HT (Cl−: 1.41 mmol) suspended in 20 cm3 of toluene with 14.1 mmol of butyl bromide at 373 K yielded 42 % butyl chloride after 15 min of reaction. In comparison, NiCl4(Et4N)2 (precursor to prepare NiCl-HT) yielded at the same conditions only 2.4 % of butyl chloride. This indicates a great mobility of Cl− in the interlayer region of HTs. The reaction rate is greatly accelerated using DMF instead of toluene and butanol totally suppressed it. This is consistent with a SN2 mechanism. The halide-exchange reaction between benzyl chloride and butyl bromide is catalyzed by both Cl-HT and NiCl-HT.

We have been exploring molecular sieve synthesis using metal complexes as templates. Our objectives were to affect the crystallization of new structures as well as prepare bifunctional catalysts via the encapsulation of metal complexes during synthesis. In this paper the results for the synthesis of SiO2, AlPO4 and SAPO molecular sieves in the presence of metallocenes will be presented. In particular, Cobalticinium ion, Cp2Co+, was found to be a template for Nonasil, AlPO4−5, AlPO4−16, SAPO−16 and CoAPO−16 which are known phases but require templates. The larger decamethyl derivative, CP*2Co+ has produced a novel high silica zeolite molecular sieve, UTD-1 as well as a new SAPO phase UTD-2 which appear to be large pore materials. In all cases, the metal complex is occluded intact and cannot be extracted. Aspects of the synthesis and characterization of these microporous materials are presented below.

The nineties have brought us to an era of environmental crisis. We are faced with problems of air pollution, both indoor and outdoor, acid rain, water pollution, hazardous wastes, toxic landfills and leaking storage tanks in our soil, to name a few. Our rapid advances into the industrial and technological age have contributed to these problems. However, our advancing technology in the areas of remediation and such “green” engineering tools as ceramic membranes can certainly make a significant contribution in terms of environmental clean-up and a healthier world.